This project is concerned with understanding extinction, the loss of learned performance that occurs when a Pavlovian signal or an instrumental action is repeatedly presented without its reinforcer. Extinction is a fundamental phenomenon of .behavior, and it provides a crucial tool used in clinical treatments designed to eliminate unwanted thoughts, emotions, and behaviors in humans. Although it is tempting to assume that extinction destroys the original learning, extinguished performance readily recovers, and several recovery effects (e.g., renewal, reinstatement, rapid reacquisition, and spontaneous recovery) indicate that the original learning may be largely intact. In addition, because these effects can be interpreted as effects of changing the background or "context," they suggest that extinction results from new inhibitory learning that is especially sensitive to the context in which it is learned. The goal of this project is to seek an integrated understanding of extinction as it is revealed in these and other response-recovery processes. Several sets of experiments with rat subjects will analyze how extinction and other forms of learning are influenced by the passage of time (a change in the "temporal context"). They will also examine ways to reduce spontaneous recovery and test a new hypothesis explaining why practice that is distributed in time may produce better learning than practice that is massed in time. Another set of experiments will analyze a different set of extinction and recovery effects (secondary extinction, concurrent recovery, and resurgence) with the goal of incorporating them in a unified account of extinction. A third set of experiments will study the effects of several drugs (d-cycloserine, yohimbine, and AM404) that are thought to have potential for facilitating extinction learning. Although such drugs hold promise as adjuncts to extinction therapy, their effects on extinction and especially the various recovery (relapse) processes under investigation here are essentially unknown at present. The results will increase our understanding of extinction, a fundamental behavioral and clinical phenomenon, and will suggest ways to help promote extinction learning so as to minimize lapse and relapse.